Signalling method and apparatus

ABSTRACT

At least one three phase driven pumps ( 56 ) in a hydrocarbon well ( 10 ) well bore ( 12 ) uses frequency shift keyed digital signals ( 78 ) to pass instructions from a surface station ( 46, 26, 34, 30 ) to a tool ( 14, 76, 56 ) and reports from a tool ( 14, 76, 56 ) to the surface station ( 46, 26, 34, 30 ) in common mode through the three phase cables ( 16 ) using a star point ( 58 ) of the three phase cables ( 16 ) after each pump as the signal transmission and reception point and as the point for coupling a DC Power supply ( 28 ), also provided in common mode on the three phase cables ( 16 ), to the down hole electronic equipment ( 72 76 ). The surface equipment ( 46 ) and the tool ( 14 ) use as a common ground. The digital messages comprises an address portion ( 80 ) identifying either the tool ( 14 ) for which an instruction ( 82 ) is destined or the tool ( 14 ) from which a report (also  82 ) originates. The digital message ( 18 ) also comprises a checksum ( 84 ) for error identification and correction.

The present invention relates to the use of electrical equipment in ahydrocarbon well. More particularly, the invention relates to signallingto and from electrical equipment, notably in a hydrocarbon productionwell. Most particularly, the present invention relates to employingthree phase power cables to transfer signals.

In downhole applications in a well bore in a hydrocarbon well, it iscommon to use an Electrical Submersible Pump (hereinafter referred to asan ESP) to pump the fluid up the well bore. It is also usual to employother electrically driven equipment, such as valves. The explanation ofthe present invention is directed towards the electrically drivenequipment being ESPs, but it is to be understood that any otherelectrically driven equipment can also be the subject of the presentinvention. The explanation of the present invention is also directedtowards the fluid being a hydrocarbon. It is to be understood that theinvention is equally applicable for any fluid, and can be water, or anychemical resource or product. The explanation of the invention is alsoparticularized on the pumping of the fluid in a vertical well. It is tobe appreciated that the invention is equally applicable to anyconfiguration of conduit, including horizontal pipes and ducts, closedor open to the atmosphere.

Returning to the example of a substantially vertical hydrocarbon well,it is desirable, for certainty of operation and optimum performance ofthe well, to monitor physical parameters such as pressures andtemperatures in the well bore, and to display such parameters at thesurface. This can be achieved by providing dedicated cables from thesurface to the well bore, for the sole purpose of operating themonitoring system. Various method exist whereby such monitoredinformation can be displayed without the need for additional cables, thephysical parameter data being transferred to the surface using theexisting cables, namely the three phase electrical supply cable which isotherwise used to supply power to drive the ESP.

International Patent Application Number WO 01/03323 A1 (Power LineCommunication System) achieves signalling by altering thecharacteristics of the inductive load of the ESP motor. Electricalconnections are made within the motor windings and a leakage current isinduced, which can be modulated using an appropriate modulation method.The leakage current induced in the windings is then detected at thesurface using a receiver that monitors the current drawn (using a methodof inductive coupling), and filters out the desired modulated signal byfiltering in the frequency domain. The present invention seeks toprovide a communication method and apparatus which improves over thatdisclosed in international Patent Application Number WO 01/03323 A1 byeliminating the need to vary the ESP load balance. The present inventionfurther seeks to provide a communication method and apparatus whichimproves over that disclosed in International Patent Application NumberWO 01/03323 A1 by removing the need to make internal connections to themotor windings and thus avoiding alterations to the ESP (or otherelectrical equipment) motor.

U.S. Pat. No. 5,670,931 (Method and Apparatus for Transmitting Data overa Power Cable Utilizing a Magnetically Saturable Core Reactor) employs amethod of communication which modifies the motor supply currentwaveform. The waveform deformations created can be detected at thesurface by monitoring the current drawn. The technique which is usedboth for creating the deformation of the waveform in the well bore,below the surface, and for detecting the deformation of the waveform atsurface, is one of inductive coupling. Inductive coupling negates theneed for a direct electrical connection onto the power supply lines.

The technique used in U.S. Pat. No. 5,670,931 is similar to that shownin Iinternational Patent Number WO 01/03323 A1 in that a characteristicof the motor load current is modified. The communication method used inU.S. Pat. No. 5,670,931 requires a physical connection to two of thewires or cables which provide the three phase motor power supply to theESP. Although this connection is not directly onto the electricalconductors, U.S. Pat. No. 5,670,931 describes using a casing that isclamped around a conductor in order to make the inductive coupling. Thepresent invention seek to provide improvement over the disclosure ofU.S. Pat. No. 5,670,931 by avoiding the need to deform existing currentwaveforms, by eliminating the need to connect to two out of three powercables, and by eliminating the need for coupling casings which furtherrestrict the small amount of space available in a well bore.

U.S. Pat. No. 5,515,038 (Data Transmission System) describes a digitaltransmission system employing a simultaneous method of communicationusing direct digital signals in a DC current loop. The communicationmethod disclosed in U.S. Pat. No. 5,515,038, in the event of a groundfault, being a DC current loop method, is, by its very nature, unable towork. The present invention seeks to provide improvement over the methodand apparatus disclosed in U.S. Pat. No. 5,515,038 by providing analternative method and apparatus which can continue to function despitethe presence of a ground fault. Further, U.S. Pat. No. 5,515,038discloses a communication system which is unidirectional, conveyingparametric data only from the well bore to the surface. By contrast, thepresent invention seeks to provide a communications method and apparatuswhich is bidirectional, allowing communication from the well bore to thesurface and from the surface into the well bore.

The DC current loop digital method of communication, described in U.S.Pat. No. 5,515,038, is limited in its capability to achieve speed oftransmission. Large value inductors are used to filter out the A.C.content of the drive power signal, and these large inductors limit thespeed of switching between logic states in the digital transmission. Bycontrast, the present invention seeks to provide a method and apparatuswith capability of much higher signalling speeds compared to thosepossible in the method and apparatus described in U.S. Pat. No.5,515,038.

U.S. Pat. No. 4,631,536 (Multiplex Submersible Pump Telemetry System)describes an A.C. (Alternating Current) based transmission system whichuses a high frequency carrier which is superimposed on the powerwaveform applied to the ESP power line which goes into the well bore.Sequencing of data then allows multiple sensor readings to be sent tosurface, encoded as digital information.

This system described in U.S. Pat. No. 4,631,536 requires connection totwo of power cables carrying the three phases of the ESP supply into thewell bore. The present invention seeks to provide improvement over thesystem shown in U.S. Pat. No. 4,631,536 by avoiding the need to connectto two out of three conductors.

The communication system described in U.S. Pat. No. 4,631,536 isone-way, from the well bore to the surface. The present invention seeksto provide improvement over U.S. Pat. No. 4,631,536 by the use of amethod and apparatus which permits bi-directional communication, fromthe surface to the well bore and from the well bore to the surface.

U.S. Pat. No. 4,631,536 does not provide tool addressing, whereby dataor commands can be addressed to or retrieved from a specifiable one of aplurality of different pumps or other devices which may be in use in awell bore. The method and apparatus disclosed in U.S. Pat. No. 4,631,536cannot therefore be configured as a common data bus system whereby onesystem can address a plurality of devices. By contrast, the presentinvention seeks to provide improvement over U.S. Pat. No. 4,631,536 byproviding for individual tool addressing, allowing data from selectableones of a plurality of individually selectable tools to be individuallyidentified. Furthermore, the present invention seeks to improve overU.S. Pat. No. 4,631,536 by providing a method and apparatus wherebycommands from the surface can be addressed to individual tools in thewell bore such that only the tool (or tools)addressed respond to acommand.

According to a first aspect, the present invention consists in a methodfor providing communications in a conduit between a control station anda communication device in the vicinity of a tool, said tool beingelectrically powered through a cable, within the conduit, said methodcomprising the steps of: generating a signal representative of a datamessage to be send; adding said signal to the power waveform on thecables; separating said signal from the power waveform on the cables;decoding said separated signal; and reconstituting said data message.

According to a second aspect, the present invention consists in anapparatus for providing communications in a conduit between a controlstation and a communication device in the vicinity of a tool, said toolbeing electrically powered through a cable, within the conduit, saidapparatus comprising: generating means operative to generate a signalrepresentative of a data message to be send; signal addition meansoperative to add said signal to the power waveform on the cables;separating means operative to separate said signal from the powerwaveform on the cables; decoding means operative to decode saidseparated signal; and reconstitution means, operative to reconstitutesaid data message.

The invention further provides that the frequency shift keyed signal canbe separated from the power waveform on the cables by one or morefrequency filters which can be at least one of a low pass filter, a highpass filter, and a band pass filter.

The invention further provides that the data message can originate atthe control station and can be received at the device, and that the datamessage can originate at the device and can be received at the controlstation.

The invention further provides that a first type of digital message canbe used for sending instructions from the control station to the device,and that a second type of digital message can be used for sendingreports from the device to the control station.

The invention further provides that a plurality of machines can be usedin the conduit; that the control station can include, in the first typeof digital message, a machine address portion indicative of the identityof the device to which an instruction is addressed; that the controlstation can send the first type of data message to all of the pluralityof devices; that each of the plurality of devices can decode the addressportion; and that a particular one of the plurality of devices canrespond to the instruction only if the address portion of the first typeof message is indicative of the first type of message being addressed tothat particular one of the plurality of devices.

The invention further provides that a plurality of machines can be usedin the well bore; that each one of the plurality of devices can include,in a second type of digital message, a report address portion indicativeof the identity of the device from which a report originates; that thecontrol station can decode the report address portion; and that thecontrol station can attribute the report to that one of the plurality ofdevices indicated by the report address.

The invention further provides that a device can provide a second typeof digital message without reception of a first type of digital message,and that the second type of digital message can be employed for at leastone of diagnostic purposes and tuning during a power up sequence.

The invention further provides that a device, from among the pluralityof devices, can provide a report only after that particular device hasreceived an instruction to provide a report.

The invention further provides that each sent data message can comprisean error detection portion containing error detection information; andthat the error detection portion in each received data message can beexamined to determine the digital integrity of the data message.

The invention further provides that the error detection portion cancontain error detection information capable of allowing for correctionof one or more errors.

The invention further provides that the error detection information caninclude a check sum.

The invention further provides that a report can contain informationabout at least one of temperature pressure, flow and vibration in thevicinity of the device.

The invention further provides that the cable can comprises at least twophases and that the signal is added to at least one of the phases.

The invention further provides that the windings to electrical equipmentwithin the conduit can be three phase, that the cables can be threephase, and that the cables are joined in a star point after passagethrough the equipment, signals from the control station to a device andsignals from a device to the control station being provided from andsent to the star point.

The invention further provides that a power supply for monitoringequipment in the well bore is connected to at least one of the cables,and that the power supply is coupled to the device via the star point.

The invention further provides that the device can have furtherattachment to a common ground, shared with the surface equipment, andthat the common ground can be the local conductive production tubingdisposed within the well bore.

The invention further provides that the conduit can be the well bore ofa hydrocarbon well and that the control station can be at the surface.

The invention is further explained, by way of an example, by thefollowing description, to be read in conjunction with the appendeddrawings, in which:

FIG. 1 is a schematic block diagram of the overall arrangement wherebyone or more downhole tools can be in communication with the surface in ahydrocarbon well.

FIG. 2A is a schematic diagram of one possible arrangement showing thedisposition of the different elements within a well bore.

FIG. 2B is a cross sectional view of one possible structure for a threephase cable 16.

FIG. 3 is more detailed schematic block diagram showing the variouscomponent parts of the signalling system

FIG. 4 is a diagram illustrating the structure of a digital message

FIG. 5 is a flow chart illustrating the activities of the downholemonitoring equipment.

And

FIG. 6 is a flow chart illustrating the activities of the surfacesignalling equipment.

Attention is first drawn to FIG. 1 showing a schematic block diagram ofthe overall arrangement of parts where a plurality of downhole tools arein communication with the surface in a hydrocarbon well.

A hydrocarbon well 10 comprises a well bore 12 (shown in dotted ourline)down which are disposed a plurality of tools 14 powered via three phasecables 16. In this example each tool 14 is shown as being connected toits own particular three phase cable. It is to be appreciated that thepresent invention also allows more than one tool 14 to be provided on athree phase cable 16. The well bore 12 is a hole, extending through theearth, perhaps for many thousands of feet. The well bore 12 is generallyof the order of 30 cm in diameter and can be a branching structure withinclined or horizontal areas rather than just a straight, vertical hole.The tools 14, although shown in FIG. 1 as being all at the same depth inthe well bore 12, are in fact disposed at different locations in thewell bore 12, being at different depths and/or in different branches ofthe well bore 12. In general terms, each of the tools 14 will be remotefrom all of the other tools 14. The three phase cables 16 are also fedinto the narrow well bore 12, there being one three phase cable 16 foreach of the tools 14.

In this example, the tools 14 are electrical submersible pumps (ESP's)used for pumping oil and/or water. It is to be appreciated that thetools 14 can be any other type of downhole powered device suitable foruse in an oil exploration or production well. The well bore 12 may be onland, or may be beneath the sea at a depth of, for example, 300 metres.

At the surface, a step down transformer 18 accepts an 11,000 volts feed20 from a distribution transformer and provides 2,000 Volts (forexample) three phase input 22 to each of a plurality of electricalswitchboards 24 which provide the three phase cables 16 to the downholetools 14.

A surface control panel 26 (also referred to herein as a “controlstation”) comprises a power supply 28 coupled to each of the three linesin each of the three phase cables 16 through a choke 30 so that each ofthe downhole tools 14 receives a common mode low DC voltage suitable forpowering downhole electronic equipment shown later in FIG. 2. The powersupply 28 can be any power source capable of powering the downholeequipment which receives and sends messages to and from a tool 14, andcan include DC supplies at a range of voltages or AC supplies, also at arange of acceptable voltages.

An AC supply 28 is preferred in this example, because the supply 28 isgenerally, if DC, subject to loss through ground faults on the cables16. However, an AC supply 28 is ground fault tolerant, and is thus thestyle of supply 28 of preference.

The purpose of each choke 30 is to provide isolation from the high(2,000 Volts) AC voltages encountered on each of the three phase cables16. The chokes 30 play no part in the signalling path of the presentinvention, and therefore do not have any influence on the signallingspeed.

A signal drive board 32 is coupled, in common mode, to each of theconductors in the three phase cable 16 through a high voltage signalisolation module 34. The signal drive board 32 can send signals to adownhole tool 14 or receive signals from a downhole tool 14.

A processor board 36 decodes received messages from the signal driveboard 32 and prepares messages to be sent by the signal drive board 32.The processor board 36 is in bi-directional communication with a centralprocessor 38 (such as a personal computer) which is the overall sourceof data to be transmitted, the overall recipient of data which isreceived, and an organ of logging, organisation and display.

The signal drive board 32 and the processor board 36 can be plug-incards or modules within the central processor 38. Equally, the centralprocessor 38 may be connected by a data link, such as an RS232 serialconnection, to the processor board 36. In another example, the centralprocessor 38 can be coupled by land line, satellite communication, radiolink or any other way from a remote point to the processor board 36. Theprocessor board 36 can be accessible through a machine accessiblecommunication facility, such as an Internet or other pageable site.

The high voltage signal isolation module 34 is situated on the signaldrive board 32 and, in each instance, comprises a high pass filter, alow pass filter and a band pass filter, as will later be described withreference to FIG. 3.

In the example of the invention given, there are shown three downholetools 14. It is to be appreciated that this does not constitute a limitupon the invention, the invention functioning equally well with just asingle downhole tool 14, or with 4, 5, 6 or even many more downholetools 14. The invention is also applicable to one, or a plurality oftools in each of a plurality of wells 10. Equally, as will be explainedlater, more than one tool 14 can be provided on each three phase cable16. The invention also works in those situations where the cable is moreor less than three phases.

Attention is next drawn to FIG. 2A, showing a schematic cross-sectionalview of one possible arrangement of components within a hydrocarbonproduction well.

The well bore 12 passes from the surface 40 through the surrounding soiland rock 42. If the hydrocarbon well 10 is at sea, there may also belayers of seawater, sand and other sediments. The well bore 12 is linedwith a metallic conducting casing 44 which contains oil or otherhydrocarbons from seeping into the surrounding soil and rock 42.

The tool 14 may be provided within casing 44, at the end of the threephase cable 16. The tool 14 is attached to a tubing 45, such as aproduction tubing, so that the production tubing 45 provides a localground reference potential. The surface equipment 46 has a coupling 48to the ESP which, in turn, is attached to a production tubing 45. Thesurface equipment 46 (which includes all of the surface electronicequipment such as the surface control panel 26) also has a grounding onthe production tubing 45. The surface equipment 46 and the tool 14 thusenjoy a common ground in the form of the production tubing 45. Thecommon ground can be any conductive member that normally can be foundextending down or within a well bore 12 and depending on the type oftool 14, it can even be casing 44.

Attention is next drawn to FIG. 2B, showing a cross sectional view ofone possible embodiment of a three phase cable 16, usable in the presentinvention.

Three conductors 39 are each surrounded by a layer of mineral insulation41 which lies within a metal sheath 43, the whole arrangement being heldtogether by armour wrapping 45. This is just one possibility. Theconductors 39 and their insulation 41 and metal sheaths 43 can bearranged in a linear fashion, or any other fashion.

Attention is next drawn to FIG. 3, showing a more detailed schematicdiagram of the tool 14, and of the signal drive board 32, connected toprovide communication between the tool 14 and the surface control panel26.

FIG. 3 includes many elements also shown in FIG. 1, and like numbersdenote like entities.

The signal drive board 32 comprises a frequency shift keying encoder 48which receives a serial string of binary data from the central processor38 via the processor board 36, converts the serial string of binary datainto a frequency shift keyed signal where a first frequency denotes abinary zero and a second frequency denotes a binary one, and feeds thefrequency shift encoded signal as an input to a drive circuit 50 whichgenerates three identical signals which are each applied to each thethree three phase cables 16 through the high voltage signal isolationmodule 34.

In the example given as the embodiment of the present invention the twofrequencies concerned are 12.674 KHz and 13.227 KHz. It is to beappreciated that the invention covers other frequencies and other bandsof frequencies. It is also to be appreciated that the present inventionis also compatible with and encompasses three tone, four-tone and other,higher order signalling systems and is not restricted to two tonefrequency shift signalling nor to binary representation of values.

The high voltage signal isolation module 34 comprises three filter units52. There is one filter unit for each three phase cable 16. A singlefilter unit 52A is to be found at the tool and is later described.

The signal drive board 32 further comprises a frequency shift decoder 54which is also coupled to the high voltage signal isolation module 34.The frequency shift decoder 54 comprises counting circuits, or a simplephase locked loop decoder to convert the frequencies of the frequencyshift key modulation into binary ones or zeros which are fed through theprocessor board 36 to the central processor 38. Reception also occurs ofFSK signals at the monitoring equipment at the tool 14, to be laterdescribed, in the same manner as at the signal drive board 32.

In this example, the frequency shift keying encoder 48 and the frequencyshift keying decoder 54 are shown as being part of the signal driveboard 32. The present invention permits the frequency shift keyingencoder 48 and the frequency shift keying decoder 54 to be situatedanywhere within the overall apparatus which is consistent with theirfunction, and a particularly advantageous place for the frequency shiftkeying encoder 48 and the frequency shift keying decoder 54 is on thesignal processor board 36.

The signals from the drive circuit 50 through the high voltage signalisolation module 34 are provided on to each of the three phase cables 16which are fed, as shown in FIG. 1, from an 11,000 Volts feed through astep down transformer 18 and a switchboard 25 to become a three phasesupply at 2,000 Volts to be fed into the well bore to the tool 14 (whichcan be one or more kilometers away)

In the well bore 12 tool 14 comprises an electrical submersible pump(ESP) 56. The three three phase cables, having passed through thewinding of the motor on the electrical submersible pump 56, join at astar point 58 beyond the electrical submersible pump 56.

The star point 58 is, if everything balances within the motor of theelectrical submersible pump 56, and if the three phase cables 16 arealso resistably balanced, a point which should, theoretically, have noresidual signal from the wave forms which drive the motor of theelectrical submersible pump 56. It is to be recollected, from FIG. 1,that the power supply 28 was fed, in common, through chokes 30, toprovide a common mode signal on the three phase cables 16. It is also tobe observed that the drive circuit 50 in the signal drive board 32provided a common mode signal on each of the three phase cables 16representing frequency encoded digital data. The star point 58 thusrepresents a point where communication signals and a power supply areprovided. The star point 58 is coupled as input to a downhole filterunit 52A which, in common with the filter units 52 to be found in thehigh voltage signal isolation module 34, comprises a high voltage highpass filter 60 followed by a low pass filter 62 and a band pass filter64. The exact parameters between the two filter units 52 52A can differ,as can voltage ratings and frequencies. However, both types of filterunit have the same function of filtering the signals from any othernoise.

In those possible embodiments where more than one tool 14 is powered byonly a single three phase cable 16, a star point 58 can be made byjoining each of the three three phase cables 16 to a virtual star point58 using equal impedances.

These three filters 60, 62, 64 provide isolation from the potentiallyhigh voltage (2,000 Volts) which drive the electrical submersible pump56 and also filter out the frequency shift keyed signal from the drivecircuit 50. There is no reason why the filters 60, 62, 64 should notalso include a band stop filter for removing the relatively lowfrequency supply (50/60 Hz) that drives the motor in the electricalsubmersible pump 56 or band pass filters for the FSK frequencies.

The output from the band pass filter 64 is coupled as input to afrequency shift decoder 54 which decodes the frequency shift encodedsignal from the drive circuit 50 and converts it into a serial stream ofbinary data which is provided as input to a microprocessor 66.

The microprocessor 66 serves much the same function as the centralprocessor 38 in the surface control panel 26. In particular, themicroprocessor 66 is coupled to monitor sensors 68 disposed in the wellbore 12 in the vicinity of the tool 14 and operatives to measure, forexample, temperature and pressure within the well bore 12, or, indeed,any other measurable parameter within the well bore 12 including, butnot restricted to, chemical properties, visible and non visible opticalproperties, density, viscosity, sound propagation rate and flow rate.

One of the functions of the microprocessor 66 is to monitor whether aninstruction from the surface control panel 66 is addressed to thatparticular tool 14. The manner in which this is done is explained later.If the microprocessor 66 discovers that an instruction to report to thesurface control panel 26 has been received, the microprocessor 66 thenreads and encodes the data from the sensors 68 and passes the data,together with other information, to a frequency shift keying encoder 48which performs the same function as the frequency shift keying encoder48 otherwise shown in FIG. 3 in the signal drive board 32. The frequencyshift keying encoded data stream is passed to a single drive circuit 70similar to each of the three drive circuits required in drive circuit50, the single drive circuit 70 passing back through the filter unit 52to drive the star point 58.

A local power supply module 72 receives the voltage from the powersupply 28 (shown in FIG. 1) via the star point 58 and converts it intomultiple power supply voltages 74 for use by the various elements 48,54, 66, 70 in the electronic module 76 within the tool 14. The wholetool 14, including the electronic module 76 and the local power supplymodule 72 uses the production tubing 45 as a local ground referencepoint.

The electronic module 76 serves as a communications device in thevicinity of the tool 14. In FIG. 3 the electronic module 76 is shown asbeing integral with the tool. In fact, the electronic module 76 needonly be near enough to the ESP 56 to send and receive signals and derivepower, in other words, the electronic module is a device in the vicinityof the tool 14. The electronic module 76 is generally referred tohereinafter as a “communication device” and may include sensors 68, inwhich case it may be generally referred to a “monitoring equipment”.

Attention is next drawn to FIG. 4 showing an exemplary message of thetype which could be sent from the surface control panel 26 to the tool14 or from the tool 14 to the surface control panel 26. The message 78comprises an address portion 80. If the message 78 comes from thesurface control panel 26 the address portion 80 indicates which of thetools 14 is to receive and interpret the message 78. If the message isto travel from a tool 14 to the surface control panel 26, the addressportion 80 indicates from which tool 14 the message originated.

The message 78 next comprises an information portion 82 which, if themessage comes from the surface control panel 26 to a tool 14, is aninstruction to be obeyed by the electronics module 76 of the tool 14and, typically, is an instruction to send the readings of the sensors68. If the message comes from a tool 14 to the surface control panel 26,the information portion 82 will typically convey indications of thereading of the sensors 68.

Of course, the message portion can convey instructions to do anythingelse, such as to switch on or switch off pieces of apparatus, to movetowards being more open or more closed if the tool is a valve, or totake different readings and, where the information portion comes from atool 14, can include readings of other variables than temperature andpressure, and can include PH, current consumed by the pump 56 or othertool, and so on.

Finally, the message 78 contains a check sum 84 which is used for errordetection and/or error correction should an error occur in the message78. In its simplest form, the check sum 84 can be a simple parity check.In its most complicated form, the check sum 84 can be any one of theerror correction and detection codes and methods used in the digitaltransmission of data.

Attention is next drawn to FIG. 5, showing a flow chart generallyindicative of one embodiment of the behaviour of the microprocessor 66in the electronic module 76 of the tool 14. The flow chart of FIG. 5assumes that an instruction is sent from the surface to thecommunication device/monitoring equipment to make the sensors 68 take areading and then transmit such readings to the surface. It is notedhowever, as previously disclosed, that a variety of instructions may besent from the surface to the communication device/monitoring equipmentand that such communication device/monitoring equipment will respond inaccordance with the instructions.

From entry 86 upon first receipt of a message, a first operation 88examines the address portion of a message 78 and compares it with thestored and known address for that particular tool 14. If a first test 90finds that there is a match, this means that the message 78 is destinedfor that particular tool 14.

A second operation 92 reads the values of the parameters measured by thesensors 68 and encodes the data as a string of binary numbers. A thirdoperation 94 then adds the address portion 80 indicative of thatparticular tool. Finally, a fourth operation 96 adds the check sum 84 tocomplete the binary digital data. A fifth operation 98 then sends theserial string of binary data to the frequency shift keying encoder 48 inthe tool 14 which goes, automatically, from there to the single drivecircuit 70 to be sent from the star point 58 after the filter unit 52through the three phase cable 16 to the surface control panel 26.

The fifth operation 98 is the end of the sending process.

Returning to the first test 90, if there is no match between the addressof the incoming message 78 and the address of the particular tool 14,this means that the message is not destined for that tool 14.Accordingly a sixth operation 100 ignores the message and a seventhoperation 102 waits, looking for incoming messages until a second test104 detects that a new message has been received when control isreturned to the first operation 88 once again to examine the addressportion 80 of the incoming message 78.

The invention permits an alternative form of operation where tool 14 canprovide a second type of digital message (a report) without reception ofa first type of digital message (an instruction), this alternative formof operation being employed for diagnostic purposes and for tuningduring a power up sequence where the FSK frequencies can be changed toavoid particular interference (new Figure). The alternative form ofoperation can also comprise transmitting sensor 68 readings at specifiedtime intervals or upon the occurrence of certain events. The data sentto the surface in this alternative form of operation is, in oneembodiment, packaged in a message 78, as previously disclosed.

Attention is finally drawn to FIG. 6 showing a flow chart of oneembodiment of the activity of the processor board 36 and/or the centralprocessor 38.

From entry 106 a third test 108 checks to see if the central processor38 is ready to send a message. If the central processor 38 is ready tosend a message, an eighth operation 110 gets the instruction that is tobe sent to a tool 14, a ninth operation 112 adds the address portion 80which designates the tool 14 which is to receive the instruction, and atenth operation 114 adds the check sum. The string of assembled binarydata is then sent to the frequency shift keying encoder 48 on the signaldrive board 32 by an eleventh operation 116. Control is then returnedback to a twelfth operation 118, described immediately below.

If the third test 108 detects that no message is currently to be sent bythe surface control panel 26, the twelfth operation 118 waits, lookingfor a received message. If a fourth test 120 detects that no message iscurrently being received, control passes back to the third test 108.Thus, in the event of nothing to do, the surface control panel 26 lookseither to send messages or to receive messages.

If the fourth test 120 detects that a message is being received, athirteenth operation 122 reads the address portion 80 of the incomingmessage, a fourteenth operation 124 reads the data in the informationportion 82, and a fifteenth operation 125 attributes the data read fromthe information portion 82 to the particular tool indicated by theaddress portion 80 of the incoming message. The processor then carriesout any operation, if necessary, as indicated in the message. Controlthen passes back to the third test 108 where the next activity isawaited.

In an alternative form of operation, the processor board 36 or thecentral processor 38 can broadcast a message to all tools 14 byemploying a default universal address portion 80 which is recognised byall tools 14, or by specific groups of tools 14, for the addressedplural tools to respond.

The invention has been described with reference to an example involvinga three phase downhole tool 14. It is to be appreciated that the presentinvention is equally applicable to use with a tool 14 which is singlephase, or any other combinations of phases and frequencies, Likewise,the tool, given in the example is Electrical Submersible Pump. It is tobe appreciated that the present invention is apt for use with any otherstyle or function of downhole device.

The present invention also has the advantage that it allows signallingto continue even when the power supply to the tool 14 is shut down.

The present invention also provides for tuning the frequencies used inthe frequency shift keyed signal. Interference, noise and other factorsmay make a particular spaced pair of frequencies unsuitable forcommunication. Accordingly, the surface control panel comprises tuningmeans, operable to select the frequency pair used by the transmissionand reception process. The tuning means firstly selects one set offrequencies for use in the frequency shift keyed signal. A test messageis then transmitted from the surface control panel to a tool. If thetool 14 signals back that the transmission of the message was adequate,the tuning means retains that set of frequencies as operatingfrequencies. If the transmission of the test message was inadequate, asindicated by the tool 14 either failing to receive the test message andfailing to respond, or signalling back either indicatively of or with anunacceptable error rate, the tuning means selects another set offrequencies to test, and so on until a successful set of spacedfrequencies is found. The selected frequencies can move in any directionin frequency, one option being exclusively upwards, another option beingexclusively downwards. Indeed, any algorithm for selecting furtherfrequencies to test is also an acceptable option.

1. A method for providing communications in a conduit between a controlstation and a communication device in the vicinity of a tool, said toolbeing electrically powered through cable, within the conduit, saidmethod comprising the steps of: generating a signal representative of adata message to be sent; adding said signal to a power waveform on thecable; separating said signal from the power waveform on the cable;decoding said separated signal; and providing the cable as three phasecable to power the tool within the conduit; creating a star point in thevicinity of the tool; and coupling signals from the control station tosaid device and signals from said device to the control station throughsaid star point.
 2. A method, according to claim 1, including the stepsof: originating said data message at said control station; and receivingsaid data message at said device.
 3. A method, according to claim 1,including the steps of: originating said data message at said device;and receiving said data message at said control station.
 4. A method,according to claim 3, including the steps of employing a first type ofdata message for sensing instructions from said control station, andemploying a second type of data message for sending reports from saiddevice to said control station.
 5. A method, according to claim 4,including the steps of: employing a plurality of tools, each in thevicinity of a respective device, in said conduit; at said controlstation, including, in said first type of data message, a device addressportion indicative of the identity of the device to which an instructionis addressed; sending said first type of data message to all of theplurality of devices; decoding said address portion at each of theplurality of devices; and a particular one of said plurality of devicesresponding to the instruction only if the address portion of the firsttype of data message is indicative of the first type of data messagebeing addressed to that particular one of said plurality of devices. 6.A method, according to claim 4, including the steps of: employing aplurality of tools, each in the vicinity of a respective device, in saidconduit; at said control station, including, in said first type of datamessage, a device address portion indicative of the identity of aplurality of addressed devices to which an instruction is addressed;sending said first type of data message to all of the plurality ofdevices; decoding said address portion at each of the plurality ofdevices; and all of said plurality of the addressed devices respondingto the instructions.
 7. A method, according to claim 4, including thesteps of: employing a plurality of tools, each in the vicinity of arespective device, in said conduit; at one of said devices, including,in said second type of data message, a report address portion indicativeof the identity of the device from which a report originates; decodingsaid report address portion at said control station; and attributing thereport to that one of said plurality of devices indicated by the reportaddress.
 8. A method, according to claim 4, including the step of adevice providing a second type of digital message without reception of afirst type of digital message.
 9. A method, according to claim 4,including the step of causing a device, from among said plurality ofdevices, to provide a report only after that particular device hasreceived an instruction to provide a report.
 10. A method, according toclaim 4, including the step of employing said second type of digitalmessage for diagnostic purposes.
 11. A method, according to claim 4,including the step of employing said second type of digital message fortuning during a power up sequence.
 12. A method, according to claim 4,including the step of employing said second type of digital message forindicating a reading from a sensor.
 13. A method, according to claim 1,including the steps of: including, in each sent data message, an errordetection portion containing error detection information; and examiningsaid error detection portion in each received data message to determinethe digital integrity of the message.
 14. A method, according to claim13, including the step of employing, in said error detection portion,error detection information capable of allowing for correction of one ormore errors.
 15. A method, according to claim 13, wherein said errordetection information includes a checksum.
 16. A method, according toclaim 1, for use where said cable comprises at least two phases, saidmethod including the step of adding said signal to at least one of saidphases.
 17. A method, according to claim 1, including the step ofcreating said start point by joining the three phase cables afterpassage through the tool.
 18. A method, according to claim 17, includingthe steps of: providing a power supply for said device; coupling thepower supply to at least one of the cables; and coupling the powersupply to said device via the star point.
 19. A method, according toclaim 1, wherein said conduit is the well bore within the hydrocarbonproduction well and wherein said control station is a surface station.20. A method, according to claim 1, including the steps of: groundingsaid device to a common ground; and grounding the control station tosaid common ground.
 21. A method, according to claim 20 wherein saidcommon ground comprises a conductive element within the well bore.
 22. Amethod, according to claim 21, wherein said conductive element compriseswell bore casing.
 23. A method, according to claim 21, wherein saidconductive element comprises tubing extending in said well bore.
 24. Amethod, according to claim 1 including the step of employing, as saidsignal representative of a data message, a frequency shift keyed signal.25. A method, according to claim 24, including the step of separatingthe frequency shift keyed signal from the power waveform on the cable byemploying one or more frequency filters.
 26. A method, according toclaim 25, wherein said one or more frequency filters includes at leastone of: a low pass filter; a high pass filter; and a band pass filter.27. A method, according to claim 24, including the step of tuning by:selecting one set of frequencies for said frequency shift keyed signal;transmitting a test message using said one set of frequencies; if saidtransmission of said test message is adequate, retaining said one set offrequencies as operating frequencies; and if said transmission of saidtest message is inadequate, selecting another set of frequencies as saidone set of frequencies.
 28. A method, according to claim 27, includingthe step of selecting a first spaced pair of frequencies as said one setof frequencies; and selecting a second spaced pair of frequencies,spaced from said first spaced pair of frequencies, as said another setof frequencies.
 29. A method, according to claim 28, wherein said secondspaced pair of frequencies is higher in frequency than said first spacedpair of frequencies.
 30. A method, according to claim 28, wherein saidsecond spaced pair of frequencies is lower in frequency than said firstspaced pair of frequencies.
 31. An apparatus for providing communicationin a conduit between a control station and a communication device in thevicinity of a tool, said tool being electrically powered through cable,within the conduit, said apparatus comprising: generating meansoperative to generate a signal representative of a data message to besent; signal addition means operative to add said signal to a powerwaveform on the cable; separating means operative to separate saidsignal from the power waveform on the cable; and decoding meansoperative to decode said separated signal; wherein said cable is a threephase cable, operative to power the tool within the conduit saidapparatus further comprising: a star point in the vicinity of the tool;and means to couple signals from the control station to said deice andsignals from said device to the control station through said star point.32. An apparatus, according to claim 31, wherein said data messageoriginates at said control station and is received at said device. 33.An apparatus, according to claim 31, wherein said data messageoriginates at said device; and is received at said control station. 34.An apparatus, according to claim 33, including means to generate a firsttype of data message from sending instructions from said controlstation, and means to generate a second type of data message for sendingrepots from said device to said control station.
 35. An apparatus,according to claim 34, further comprising: a plurality of tools, each inthe vicinity of a respective device, in said conduit; at said controlstation, means to include, in said first type of data message, a deviceaddress portion indicative of the identity of the device to which aninstruction is addressed; broadcast means, operative to send said firsttype of data message, a device address portion indicative of theidentity of the device to which an instruction is addressed; broadcastmeans, operative to send said first type of data message to all of theplurality of devise; device address decoding means operative to decodesaid device address portion of each of the plurality of devices; andresponse means, operative to cause a particular one of said plurality ofdevices to respond to the instruction only if the device address portionof the first type of data message is indicative of the first type ofdata message being addressed to that particular one of said plurality ofdevices.
 36. An apparatus, according to claim 34, further comprising: aplurality of tools, each in the vicinity of a respective device, in saidconduit; at said control station, means to include, in said first typeof data message, a device address portion indicative of the identity ofa plurality of addressed devices to which an instruction is addressed;broadcast means, operative to send said first type of data message toall of the plurality of devices; device address decoding means,operative to decode said device address portion at each of the pluralityof devices; response means, operative to cause all of said plurality ofaddressed devise responding to the instruction.
 37. An apparatus,according to claim 34, comprising: a plurality of tools, each in thevicinity of a respective device, in said conduit; at any one of saiddevices, means to include, in said second type of data message, a reportaddress portion indicative of the identity of the device from which areport originates; report address decoding means, operative to decodesaid report address portion at said control station; and attributionmeans, operative to attribute the report to that one of said pluralityof devices indicated by the report address.
 38. An apparatus, accordingto claim 34, wherein a device is operative to provide a second type ofdigital message without reception of a first type of digital message.39. An apparatus, according to claim 34, wherein a device, from amongsaid plurality of devices, is operative to provide a report only afterthat particular device has received an instruction to provide a report.40. An apparatus, according claim 34, wherein said second type ofdigital message comprises diagnostic data.
 41. An apparatus, accordingto claim 34, wherein said second type of digital message comprises datafor tubing the apparatus.
 42. An apparatus, according to claim 34,wherein said second type of digital message comprises data indicative ofa reading from a sensor.
 43. An apparatus, according to claim 31,comprising means to include, in each sent data message, an errordetection portion containing error detection information; and furthercomprising examination means operative to examine said error detectionportion in each received data message and to determine the digitalintegrity of the message.
 44. An apparatus, according to claim 43,wherein said error detection portion comprises error detectioninformation capable of allowing for correction of one or more errors.45. An apparatus, according to claim 43, wherein said error detectioninformation includes a checksum.
 46. An apparatus, according to claim31, where said cable comprises at least two phases, and where saidsignal addition means is operative to add said signal to at least one ofsaid phases.
 47. An apparatus, according to claim 31, wherein said starpoint comprises junction of the three phase cables after passage throughthe tool.
 48. An apparatus, according to claim 47, further comprising: apower supply for said device; means to couple the power supply to atleast one of the three phase cables; and means to couple the powersupply to said device via the star point.
 49. An apparatus, according toclaim 31, wherein said conduit is the well bore within a hydrocarbonproduction well and wherein said control station is a surface station.50. An apparatus, according to claim 31, further comprising: a commonground; means to ground said device to said common ground; and means toground the control station to said common ground.
 51. An apparatus,according to claim 50 wherein said common ground comprises a conductiveelement within the well bore.
 52. An apparatus, according to claim 51,wherein said conductive element comprises well bore casing.
 53. Anapparatus, according to claim 51, wherein said conductive elementcomprises tubing extending in said well bore.
 54. An apparatus,according to claim 31, wherein said signal representative of a datamessage, is a frequency shift keyed signal.
 55. An apparatus, accordingto claim 54, including means to separate the frequency shift keyedsignal from the power waveform on the cable comprising one or morefrequency filters.
 56. An apparatus, according to claim 55, wherein saidone or more frequency filters includes at least one of: a low passfilter; a high pass filter; and a band pass filter.
 57. An apparatus,according to claim 54, further comprising tuning means: said tuningmeans being operative to select one set of frequencies for saidfrequency shift keyed signal; said tuning means being operative totransmit a test message using said one set of frequencies; if saidtransmission of said test message is adequate, said tuning means beingoperative to retain said one set of frequencies as operatingfrequencies; and if said transmission of said test message isinadequate, said tuning means being operative to select a another set offrequencies as said one set of frequencies.
 58. An apparatus, accordingto claim 57, wherein said tubing means is operative to select a firstspaced pair of frequencies as said one set of frequencies; and whereinsaid tuning means is operative to select a second spaced pair offrequencies, spaced from said first spaced pair of frequencies, as saidanother rest of frequencies.
 59. An apparatus, according to claim 58,wherein said second spaced pair of frequencies is higher in frequencythan in said first spaced pair of frequencies.
 60. An apparatus,according to claim 58, wherein said second spaced pair of frequencies islower in frequency than said first spaced pair of frequencies.